American History 201

Native Americans living in the Amazon bear an unexpected genetic connection to indigenous people in Australasia, suggesting a previously unknown wave of migration to the Americas thousands of years ago, a new study has found.

“It’s incredibly surprising,” said David Reich, Harvard Medical School professor of genetics and senior author of the study. “There’s a strong working model in archaeology and genetics, of which I have been a proponent, that most Native Americans today extend from a single pulse of expansion south of the ice sheets—and that’s wrong. We missed something very important in the original data.”

Previous research had shown that Native Americans from the Arctic to the southern tip of South America can trace their ancestry to a single “founding population” called the First Americans, who came across the Bering land bridge about 15,000 years ago. In 2012, Reich and colleagues enriched this history by showing that certain indigenous groups in northern Canada inherited DNA from at least two subsequent waves of migration.

The new study, published July 21 in Nature, indicates that there’s more to the story.

Pontus Skoglund, first author of the paper and a postdoctoral researcher in the Reich lab, was studying genetic data gathered as part of the 2012 study when he noticed a strange similarity between one or two Native American groups in Brazil and indigenous groups in Australia, New Guinea and the Andaman Islands.

“That was an unexpected and somewhat confusing result,” said Reich, who is also an associate member of the Broad Institute of Harvard and MIT and a Howard Hughes Medical Investigator. “We spent a really long time trying to make this result go away and it just got stronger.”

Skoglund and colleagues from HMS, the Broad and several universities in Brazil analyzed publicly available genetic information from 21 Native American populations from Central and South America. They also collected and analyzed DNA from nine additional populations in Brazil to make sure the link they saw hadn’t been an artifact of how the first set of genomes had been collected. The team then compared those genomes to the genomes of people from about 200 non-American populations.